The notal organ of the scorpionfly (Panorpa vulgaris): an adaptation to coerce mating duration

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Abstract
The notal organ in P. vulgaris (Insecta: Mecoptera) is a clamplike structure on the dorsum of the middle of the male’s abdomen that holds one of the female’s forewings throughout mating. Males often provide salivary masses as food to their mates during mating, and a male’s ability to produce saliva depends upon whether he has fed adequately before mating. To test the hypothesis that the evolutionary function of the notal organ is to coerce longer matings than are in the interests of females, the notal organ and the amount of food males and females receive before mating were experimentally manipulated. In support of the hypothesis, copulation was reduced when the notal organ was made inoperative under the following four conditions: (1) female fed and male starved before mating, no saliva during mating; (2) same as in condition 1 but with one salivary mass during mating; (3) both sexes starved before mating, no salivary mass during mating; and (4) both sexes fed before mating. However, when females were starved before mating and males were fed, resulting in multiple masses being provided during mating, the notal organ had no effect on length of copulation, and thus there was no sexual conflict over mating duration. In addition, the larger the female relative to her mate, the briefer the copulation when the notal organ was operative, which suggests that a physical struggle between the male and female may occur during sexual conflict about mating duration. This is one of only a few studies that provide evidence of adaptation to the domain of sexual coercion. [Behav Ecol 1991;2:156–164]

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